Phonation is a component of speech communication with a highly complex interplay of physiological and physical properties. Phonation is the vibratory system in the larynx that changes air flow from the lungs into sound in the throat. The process of vocal fold vibration and the conversion of air flow into sound is insufficiently understood for the purposes of making precise diagnostic decisions in the voice clinic, targeting optimal intervention strategies for voice problems, and achieving high quality articulatory speech synthesis. The long range goal of the proposed research program is to determine an optimal numerical model of phonation for normal and pathological conditions, where the complexities of both tissue and flow-acoustic dynamics are taken into account. The focus of this research proposal is to resolve basic issues related to the aerodynamics and acoustics of phonation. Those issues include (1) the relevance of quasi steady assumptions and steady flow modeling, (2) the effects of turbulence, flow separation, and moving glottal walls, and (3) the effects of flow-acoustic interactions. Once the details of the basic physics are determined, the criteria for a highly effective numerical model of phonation can be established. Two general types of models are used to study these issues, numerical and physical. The physical models (both static and dynamic) will generate data to validate the numerical methods, as well as to directly study basic physics related to phonation. The numerical methods (both static and dynamic) will provide detailed information linking the glottal aerodynamics to the intraglottal pressures and the creation of sound at the glottal exit. The effects are studied for a wide range of glottal conditions with and without the presence of vocal tract loading. The research program is a collaboration between the Voice Research Laboratory at Bowling Green State University and the Ray Herrick Laboratories and the Thermal Sciences and Propulsion Center at Purdue University.